Ultra high frequency apparatus



March 29, 1949. GUREWlTSCH 2,465,801

ULTRA HIGH FREQUENCY APPARATUS Filed NOV. 20, 1944 Fig.2. Fig.3.

Fig.4. I -Fig.5.

Inventor": An atole M. Gurewibsch,

b9 WW His Attzcmneg.

Patented Mar. 29, 1949 UNITED STATES ENT OFFICE 2,465,801 ULTRAHIGH FREQUEficY APPARATUS AnatoleflM. Gurewitsch, Schenectady, N.'Y., as-

signor to General Electric Companwa corpora tion of New York Application November" 20, 1944, Serial No. 564,383 3 Claims. (01. its-44) This invention relates to high frequency apparatus and is concerned primarily with the provision of new and improved means and methods for obtaining wide band modulation of cavity resonator circuits such as are employed in ultra high frequency amplifiers and oscillators.

When operating high frequency cavity resonator circuits as ultra high frequency amplifiers and oscillators and employing plate modulation to obtain wide band modulation of the resonators, it has been found that the capacity which ultra high frequency chokes or by-pass condensers normally introduce across the source of modulation makes most diflicult and, in many cases prac tically impossible, the obtaining of Wide band modulation. vcntion, therefore, to provide an improved ultra high frequency choke for use in cavity resonators.

, It is a further object of the present invention to provide a new and improved ultra high frequency choke which istunable over a broad range. It is a still further object of the presentinvention to provide a new and improved high impedance choke for a cavity resonator which has a minimum capacity to ground and which does not" add to the interelectrode capacitance of an electronic tube used in the resonator.

An important feature of the present invention consists in the use of an ultra high frequency choke Within a tubular anode of an electron discharge device used in a cavity resonator, the

choke being placed essentially entirely within a' region surrounded by the anode so that the component parts thereof having a minimum capacity to other elements of the resonator and, specifically, do not add to the anode-grid or anodeground capacitance of the discharge device.

The features of the invention desired to be protected herein are pointed out in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood byreference to the following description taken in connection with the drawing in which Fig. l is a sectional view' of an ultra high frequency oscillator-modulator employing" cavity resonator circuits suitably embodying the invention, and Figs. 2-5 illustrate modificationslof the ultra high frequency choke employed in the system of Fig. 1

Referring particularly to Fig. 1, there is shown an oscillator of the re-entrant cavity resonator type, which has as its central element a high fre:

quency electron. discharge device such as the triode l comprising spacedplanar electrodes including an anode 2, a' control grid 3', anda cath- It is an object of the present instructures.

cylindrical structures having their electron re-' ceiving and emitting surfaces, respectively, at the opposed ends of the axially aligned cylindrical The grid or control electrode 3 is supported in spaced'relation between the active surfaces of the. anode and cathode by means of a metallic disk 5 which forms an external connection for the grid. Vitreous members 6, I are sealed between the anode and grid and the cathode and grid, respectively, to support the electrodes in spaced relation and form an enclosing envelope for the electron discharge path of the tube. The cathode 4 may be heated by the usual filament (not shown) supplied with heating current over a transmission line having an inner conductor 8 and an outer conductor 9, and the outer conductor 9 may serve as an external connection for the cathode. tions to the anode are made over a conductor Ill which likewise serves as means for supplying modulating potentials to the anode circuit,

The operatingsystem in which the tube l is incorporated comprises a cavity resonator structure having as its principal component an elongated conductive member illustrated as cylinder ll and formed, for example, of copper or brass preferably silver plated. This cylinder surrounds the tube I and is symmetrical with respect to the axis of alignment of the electrodes of the tube. one end of the cylinder I l and is provided with an inwardly directed portion I3 which engages the outer surface of the cathode 4, the resilient fingers Hio'f the part ls providing a mount for the tube l The cavity resonator defined by the cylindrical conductor H is of the concentric conductor type and the part l3 forms a'portion of the inner conductor of this resonator. The remainder of the'inner conductor comprises a conductive tube l5, provided with s'pring fingers I5 which engage the outer surface of anode 2, and an additional longitudinal conductive tube Fl, the adjacent ends of the conductive tubes l5, l1 being spaced apart by a sm'all'insulating gap l8;

1 The grid disk 5 is peripherally connected to a tubular conductor l 9' and through that conductor with a terminal wire 20 which extends through an insulating bead 2 lprovided in a wall of cylinder H and is connected to one terminal of an external bias resister 22, the other terminal of the resistor being connected to the outer surface of the member ll. The tubular conductor [9 is supported by a plurality of posts or insulators 231'. The left-hand end of the tubular conductor Direct current connec- A conductive wall part [2 extends across I9 is Spaced from the end wall I2 and the righthand end of the conductor I9 is made adjustable in length by means of an additional tubular conductor 24 provided with spring fingers 25 for engaging the outer surface of conductor I9 and slidable along that outer surface, its position being adjusted by means of an external rod 26. The dimensions of the cavity resonator defined by the cylinder I I and the inner conductor comprising members I3, I5, I! may be adjusted by means of a plunger 21 having two sets of contact fingers 28, 29 which respectively bear upon the opposed surfaces of the parts II, II. The plunger may be moved back and forth by an externally accessible actuating rod 30 and, by this means, the size of the resonant cawty may be adjusted as desired.

Viewing the structure of Fig. l as a device for generating sustained oscillations, it may be noted that the triode I comprises means for exciting the system provided by the cylinder II. When voltage variations are caused to occur between the grid and anode of the tube I at the resonant frequency of the cavity resonator I I, as modified by the presence of the tubular conductors I9, 24 and the tube I, electromagnetic waves of the frequency in question Will be established in the resonator defined by the inner and outer concentrio conductors. Such waves may be considered as being initiated in the vicinity of the grid-anode gap and as being propagated from this point throughout the remainder of the resonator. Their path of propagation is governed by the presence of the conductive tubes I9, 24 which tend to confine or guide the waves along the annular space between these tubes and the conductors I5, I'I. At the extremity of the tube 24, the waves are free to pass through the region bounded by the outer surfaces of the conductors I9, 24, the cylinder H and the plunger 21. Wave energy issuing from Within the tubes I9, 24 can fiow in the reverse direction along the outside of these conductors to the vicinity of the cathode-grid gap of the triode I. When desired phase or magnitude relationships of the waves supplied from the gridanode gap to the grid-cathode gap are established, regenerative oscillations are produced. The oscillator may also be operated as a plate modulator by supplying modulated potentials to the conductor I connected to the anode 2.

In order that high frequency energy may be taken from the cavity resonator for utilization in an external circuit, there is provided an output electrode which is illustrated, for example, as of the capacitive type which comprises a probe or disk 3| which extends into the resonator adjacent the outer surface of tubular conductor I9 and which is supported from a conductor 32 which forms the inner conductor of a concentric transmission line, the outer conductor 33 of the line being conductively connected to cylinder II.

In order to prevent ultra high frequency energy within the cavity resonator from flowing through gap I8 and the undesired path established between the conductors I0 and H, a, choke is provided and comprises the cavity resonator defined by the inner surface of tubular conductor I and the outer surface of conductor I0 and tuned by means of a plunger 34. The plunger 34 bears two sets of contact fingers 35, 36 which respectively engage the opposed surfaces of the conductors I5, I0. The plunger 34 may be moved back and forth for tuning the cavity resonator by an externally accessible actuating rod 31. By ad justment of the position of plunger 34, the choke is made resonant at a quarter wave length mode of the high frequency oscillations established Within the principal cavity resonator. The result is that a high impedance is created in series with the concentric transmission line formed by conductor I0 and the inside of tubular conductor I1. Leakage of high frequency energy to the outside is made negligible as a consequence. One of the advantages of the high frequency choke thus formed is that the resultant capacity between ground and the source of modulation connected to conductor I0 consists only of the capacity across the gap I8 between adjacent ends of conductors I5, I1 in parallel with the capacities which exist between conductors I0 and I5 and the grounded cylinder II These latter capacities may be made reasonably small so that, as a result, all ultra high frequency currents are guided to the cavity resonator and all modulating frequencies and unidirectional currents are maintained in their proper channels and good modulation obtained.

An additional advantage of the ultra high frequency choke consists in the structure by which all metallic parts of the choke are placed inside the conductive tube I5, which functions as an extension of the anode 2, and, as a result, have no effect on the low frequency capacity of the anode, since the region within the tube I5 is essentially completely shielded for low frequency currents.

A modification of the ultra high frequency choke which is particularly useful when the 0scillator operates at low frequencies is illustrated in Fig. 2, in which the physical size of the cavity resonator or choke in the extended anode member 38 is reduced by a tunable foreshortening capacity. The member38 engages at one end the outer surface of anode 2 and at its other end is provided with a disk 39 attached to this inner surface. A disk or plate 40, slidable along the conductor I0 by means of actuating rod 31, forms with disk 39 a tuning capacitance which not only foreshortens the length of the cavity resonator but permits use of this type of choke over a wide frequency range. A particular advantage of this structure is that ultra high frequency voltage alone and no unidirectional voltage is developed across the capacity which exists between plates 39, 40.

In the modification of the ultra high frequencychoke shown in Fig. 3, small physical size of the choke is achieved by folding the concentric transmission line resonator several times. This folding is obtained by using a pair of tubular conductors 4|, 42 concentrically positioned within the extended anode conductor 43. The conductor 42 has an end wall 44. Preferably, in this form of the choke the member 42 is fixed upon the conductor I0 so that the choke operates at a fixed frequency determined by the effective electrical length of the sinuous concentric transmission line formed by the folded conductors 4 I 43. This frequency obviously is considerably lower than the frequency obtainable with the chokes illustrated in Figs. 1 and 2.

Fig. 4 illustrates an arrangement of wave chokes in series to cover a wide frequency band without requiring any adjustment or positioning of the members of individual chokes. In this form of the invention, the hollow extended anode cylinder 45 concentrically surrounds a plurality of cup-shaped conductors 46-48. The conductors 46-48 are of different lengths and the length of each of the conductors is selected to equal a quarter wave length at a desired frequency in the frequency band to be covered by the ultra high frequency apparatus with which the choke is employed.

In the form of the invention shown in Fig. 5 there is illustrated an arrangement of a plurality of chokes which is electrically equivalent to that of the arrangement of Fig. 4 with the exception that the arrangement of Fig. 5 is physically more compact. In this modification, the conductive cylinders 49, 50, concentrically disposed about the conductor i and within the extended anode cylinder are of different lengths and the concentric transmission line resonators defined by the inner and outer surfaces of respective pairs of these conductors act to suppress the flow of ultra high frequency energy between the conductors l0 and H at different points in the frequency band covered by the apparatus with which the choke is employed. In all of the structures shown in Figs. 1-5, the conductor l0 may be hol low and may serve to supply cooling fluid to the anode of the electron tube I.

It is apparent that, by placing the metallic elements of the ultra high frequency choke essentially entirely within a region surrounded by an active conductor of the cavity resonator with which it is employed, minimum capacity between these elements and the remaining conductors of the ultra high frequency circuits is established. Specifically, in the forms illustrated, the choke, by being contained inside a conductive cylinder attached to the anode and operating at the same unidirectional potential, does not increase either the capacity between the anode and grid of the tube l or the capacity which exists between the anode and the grounded tubular conductor ll. Moreover, since the active elements of the choke are all maintained at the same unidirectional potential, the total unidirectional capacity of the resultant choke is kept at a minimum value with resultant improved operation of the high frequency apparatus either as a modulator or as an amplifier.

While the invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a high frequency resonator comprising a tubular outer conductor, a hollow inner conductor concentrically supported within said outer conductor, a section of said inner conductor being operated at a unidirectional potential difference with respect to said outer conductor and being separated from the remainder of said inner conductor by an insulating gap, a

lead-in conductor conductively connected to said section and concentrically supported within said inner conductor to form therewith a section of concentric transmission line, and means within said section of said inner conductor for tuning the section to prevent leakage of energy from said resonator through said gap.

2. Ultra high frequency apparatus comprising a tubular outer conductor and a centrally disposed tubular inner conductor, said conductors defining a high frequency resonator, means for exciting said resonator, said inner conductor including a portion operated at a unidirectional potential difference with respect to said outer conductor and the remainder of said inner conductor and being separated from said remalnder by an insulating gap, a leadin conductor to said portion concentrically supported within said inner conductor to form therewith a section of concentric transmission line, and means for preventing flow of high frequency energy from said resonator through said gap and said transmission line comprising an adjustable plunger within said portion for tuning said portion to the resonance frequency of said resonator.

3. Ultra high frequency apparatus comprising a, tubular outer conductor and a centrally disposed tubular inner conductor, said conductors defining a high frequency resonator, means for exciting said resonator, said inner conductor including a portion operated at a unidirectional potential difference with respect to said outer conductor and the remainder of said inner conductor and being separated from said remainder by an insulating gap, a lead-in conductor to said portion concentrically supported within said inner conductor to form therewith a section of concentric transmission line, and means for preventing fiow of high frequency energy from said resonator through said gap and said transmission line comprisin a plunger conductively connected between the inner surface of said portion and said lead-in conductor for adjusting the length of the transmission line defined by said lead-in conductor and said portion to a value equal to a quarter wave length at the operating frequency of said resonator.

ANATOLE M. GUREWITSCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,322,971 Roosenstein June 29, 1943 2,392,664 Gurewitsch Jan. 8, 1946 2,408,355 Turner Sept. 24, 1946 2,412,805 Ford Dec. 17, 1946 2,416,080 Bailey Feb. 18, 1947 2,421,784 Haeseler June 10, 1947 

